Hi want to delete the snow leopard I have installed on my Hackintosh and replace with Ubuntu via USB as don't have access to cd drives. Please help!
Yours probably counts as a repeat question, but I'll assume you searched the forums and couldn't find what you need.
1) Download LiveUSB version of Ubuntu of your choice and put it on a USB (for PC, unless you changed the boot system?) I like Unetbootin for this, there is a Mac OS X version. See https://help.ubuntu.com/community/Installation/FromUSBStick
2) Boot Mac OS X installer, go to Disk Utility, click the OS X partition, Erase.
3) Hope and pray the LiveUSB version you got works. CHECK THE MD5SUM on your Ubuntu ISO before you delete OS X!
As a safer option, you might try partitioning your drive in disk utility and dual-booting. If you're asking this question you probably shouldn't be single-booting Linux. It's the sad truth that PC makers still don't necessarily take Linux users into account when releasing firmware upgrades, and there's a minor chance you will at some point want some other OS on there as a backup. I wish that were not the case and it's pretty rare, but it is a risk. There are plenty of users who know enough they can get away with single-booting a linux distro, but I am not one of them. (For example, as far as I know the only way to set up an Airport device is through OS X...I can use it in Ubuntu but for the initial setup I have to go through the Mac interface.)